A mounting support and fluid interfacing connection between process conduits of differing pressure and an instrument capable of sensing the differing pressure and providing a signal indicative of the pressure differential of the process medium contained within the conduits. The mounting support, in addition to providing structural support for the differential pressure sensing apparatus, serves to transmit pressure to the high and low pressure portions of the differential pressure sensing mechanism. The support may also include valves for controlling fluid pressure communication in the high and low range pressure transmitting passages and for establishing a balanced pressure condition between the low pressure and high pressure sides of the differential pressure sensing mechanism for the purpose of calibration.